For example, when cutting threads of a male screw made of a pipe with a cutting tool, chattering of the tool may cause flaws such as chattering flaws on the threads. It has conventionally been the usual practice to depend on an operator's visual inspection for the detection of these flaws on threads of a male screw, and this has involved the following problems:
(1) It is difficult to ensure certain detection of flaws on threads. PA0 (2) Visual inspection requires a high degree of attention, resulting in considerable fatigue of the operator. PA0 (3) The detecting operation requires a long time and is not therefore efficient. PA0 (1) Unless the light from the light source is applied onto the roots of the threads, it is impossible to detect a flaw on the tops, the roots and the flanks of the threads of the male screw, if any. PA0 (2) Even threads with no flaws may be erroneously judged as having flaws because of dirt or dust depositing on the tops of the threads. PA0 uniformly applying a light onto substantially the entire surface of threads of a male screw in the axial direction thereof and at least part of the surface of said threads of said male screw in the circumferential direction thereof while rotating said male screw at a prescribed circumferential speed around the axis thereof; PA0 continuously measuring, during one turn of said male screw around the axis thereof, electric signal values corresponding to variations in brightness of the surface of said male screw in the axial direction thereof, which are caused by tops, roots and flanks of said threads of said male screw onto which said light is applied; PA0 obtaining an average value of the thus measured electric signal values corresponding to said variations in brightness of said male screw in the axial direction thereof; and PA0 comparing the thus obtained average value of said electric signal values with a previously set reference value, to detect a flaw on said threads of said male screw; PA0 characterized by: PA0 fully applying said light onto the tops, the roots and the flanks of said threads of said male screw; and PA0 said obtaining step of said average value of said electric signal values comprises:
As an apparatus for solving the above-mentioned problems and accurately detecting a flaw on threads of a male screw, the following apparatus for detecting a flaw on threads of a male screw is disclosed in Japanese Patent Provisional Publication No. 54-150,163 dated Nov. 26, 1979, which comprises:
a rotating means for rotating a male screw at a prescribed circumferential speed around the axis thereof; a light source for uniformly applying a light onto substantially the entire surface of threads of said male screw in the axial direction thereof and at least part of the surface of said threads of said male screw in the circumferential direction thereof, said light source being provided at such a position that the optical axis obliquely intersects the axis of said male screw so that said light from said light source is not applied onto roots of said threads of said male screw; a photoelectric converter for continuously measuring, during one turn of said male screw around the axis thereof, a brightness distribution of said male screw corresponding to tops of said threads of said male screw in the axial direction thereof onto which said light from said light source is applied; and an information processing means for continuously comparing, during said one turn of said male screw, said brightness distribution of said male screw as measured by said photoelectric converter with a previously set reference brightness distribution, to detect a flaw on said threads of said male screw (hereinafter referred to as the "prior art").
However, the above-mentioned prior art, in which a flaw on threads of a male screw is detected by the inconsistency between the reference brightness distribution and the brightness distribution of the male screw in the axial direction thereof as measured by the photoelectric converter, which occurs when the light from the light source is applied onto the roots of the threads, involves the following problems:
Under such circumstances, there is a strong demand for a method and an apparatus for ensuring rapid detection of flaws such as chattering flaws produced on tops, roots and flanks of threads of a male screw, but such a method and an apparatus have not been proposed as yet.